The invention relates to a biometric sensor having a sensor chip and a chip housing, into which the sensor chip is inserted, and to a method for its production.
It is known to record features specific to a person, for example finger minutiae, that is to say fingerprints, for the authentication of persons. Such an authentication of persons can be used, for example, in mobile telephones, computers, motor vehicles, keys, etc. In certain fields of application, in particular in mobile telephones, it is necessary to configure the chip housing to be as small as possible, in order to permit incorporation. In particular, in this case a minimum component thickness is desirable.
Published, European Patent Application EP 0 789 334 A2 discloses a biometric sensor in which a sensor chip is fitted to a leadframe. The sensor chip has an electrical contact made with it by a wire-bonding method and, by a molding compound is encapsulated in such a way that the sensor surface is accessible through an appropriate cutout in the molding compound. The disadvantage in this known sensor is that, first, it is still relatively large and, second, it is relatively complicated to produce.
It is accordingly an object of the invention to provide a biometric sensor and a method for its production that overcome the above-mentioned disadvantages of the prior art devices and methods of this general type, which has the lowest possible size and is simple to fabricate.
With the foregoing and other objects in view there is provided, in accordance with the invention, a biometric sensor. The biometric sensor contains a housing, connecting leads disposed on or in the housing, and a sensor chip disposed in the housing. The sensor chip has a top, a field sensor, and connecting contacts in a form of electrically conductive bumps, the electrically conductive bumps making contact with the connecting leads and have a given height. A scratch protection covering is disposed on the top of the sensor chip. An adhesive layer is disposed between the scratch protection covering and the housing. The adhesive layer is disposed at least around the sensor field, the adhesive layer has a thickness matched to the given height of the electrically conductive bumps creating a leak-tight connection between the sensor chip and housing.
It is characteristic of the biometric sensor according to the invention that the chip housing already has connecting contacts for the sensor chip at predetermined points. When it is inserted into the chip housing with the bumps (knob-like elevations of conductive material) located at appropriate points, the chip is automatically brought into connection with the connecting contacts belonging to the chip housing, so that subsequent wire bonding is dispensed with completely. The sensor chip is seated firmly and tightly in the chip housing, so that it is also possible to dispense completely with the molding, that is to say the encapsulation of the chip with a plastic compound. Furthermore, the biometric sensor according to the invention can be produced in a very simple, quick and low-waste manner. A particular advantage in this case is that contact making between the bumps and the connecting contacts belonging to the chip housing, and sealing between the chip housing and the sensor chip by the adhesive layer are carried out in one operation. Since the sensor chip according to the invention does not have to be encapsulated from both sides either, and the separate chip housing can be matched exactly to the geometry of the sensor chip and the subsequent field of use of the sensor, the sensor according to the invention can also be made significantly smaller than previously conventional sensors, given a predefined sensor surface.
According to an advantageous embodiment, in addition to the bumps in contact with the connecting leads, at least one further supporting bump is provided on the top of the sensor chip at a point which prevents the sensor chip from tilting relative to the chip housing. A xe2x80x9cdummy bumpxe2x80x9d of this type ensures that the sensor chip, after being inserted into the corresponding depression in the chip housing, is aligned in the same plane as the chip housing. This ensures a satisfactory contact between all the bumps on the sensor chip and the corresponding connecting contacts belonging to the chip-housing connecting leads.
The adhesive layer expediently is formed of a frame-like circumferential adhesive film that is applied around the sensor surface of the sensor chip.
According to an advantageous embodiment, the chip housing is an injection-molded housing, the connecting leads being embedded in the material of the chip housing and being routed to an outer edge of the chip housing. This permits subsequent damage to the connecting leads to be avoided. The connecting leads emerging at the outer edge of the chip housing form the leads or pins, which can be configured as plug-in, solder-in or clamp contacts.
With the foregoing and other objects in view there is further provided, in accordance with the invention, a method of producing a biometric sensor. The method includes the steps of:
a) providing a wafer having sensor chips with connecting contacts;
b) applying conductive bumps to the connecting contacts of the sensor chips;
c) covering a front side of the wafer with a scratch protection covering;
d) removing the scratch protection covering from over a top of the conductive bumps;
e) separating the sensor chips from one another;
f) applying an adhesive layer around a sensor field of a respective sensor chip, the adhesive layer having a thickness being matched to a height of the conductive bumps such that, in a subsequent method step, a leak-tight connection between the sensor chip and a chip housing is created;
g) introducing the sensor chip into the chip housing, the chip housing having electrical connecting leads disposed one of in and on the chip housing; and
h) carrying out simultaneously an adhesive bonding of the respective sensor chip to the chip housing and making contact between the conductive bumps and the electrical connecting leads belonging to the chip housing.
It is therefore characteristic of the method according to the invention that, as early as during the wafer production process, appropriate bumps, that is to say knob-like conductive elevations, are applied to the sensor-chip connecting contacts of the wafer. This can be carried out, for example, by screen printing. The top (front side) of the wafer is subsequently provided with a preferably transparent scratch protection covering, whose layer thickness is matched to the bump height. The bumps are then freed from the scratch protection covering and any oxide layer that may be present, preferably by using a chemical mechanical polishing process (CMP). At the same time, this step achieves equalization of the bumps, that is to say coplanarity between the bumps is produced, which improves the ability to make contact in the subsequent processes. Following the separation of the sensor chips, an adhesive medium, preferably an adhesive film, is applied around the sensor surface, its thickness being matched to the bump height. The sensor chip is then mounted in a housing corresponding to the product requirements, preferably in an injection-molded plastic housing, the adhesive bonding of the sensor chip to the chip housing and the making of electrical contact between bumps and chip housing being carried out in one step.
In the method according to the invention, therefore, the equalization of the bumps to achieve coplanarity and the removal of the protective layer and the oxide layer is carried out at the wafer level. Making contact between the bumps and the chip housing, and sealing between the chip housing and sensor chip are carried out in a single operation. In this way, the sensor can be produced in a very simple and cost-effective manner and with very small dimensions.
As an alternative to the method in which the entire front side of the wafer is covered with a scratch protection covering, and the scratch protection covering is subsequently removed again from the top of the bumps, it is also possible to apply the scratch protection covering to the front side of the wafer in such a way that, by suitable masking in the area of the bumps, openings in the scratch protection covering are kept free, the mask subsequently being removed again.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a biometric sensor and a method for its production, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.